java树结构stream工具类的示例代码详解

package com.example.demo.entity;

import lombok.AllArgsConstructor;

import lombok.Builder;

import lombok.Data;

import lombok.NoArgsConstructor;

import java.util.List;

@Data

@Builder

@AllArgsConstructor

@NoArgsConstructor

public class Menu {

     /**

      * id

      */

     public Integer id;

      * 名称

     public String name;

      * 父id ，根节点为 0

     public Integer parentId;

      * 子节点信息

     public List<Menu> childList;

     public Menu(Integer id, String name, Integer parentId) {

         this .id = id;

         this .name = name;

         this .parentId = parentId;

     }

}

package com.example.demo.util;

import cn.hutool.json.JSONUtil;

import com.example.demo.entity.Menu;

import java.util.Arrays;

import java.util.List;

import java.util.Objects;

import java.util.stream.Collectors;

public class TreeUtil {

     /**

      * 递归查询子节点

      *

      * @param root 根节点

      * @param all  所有节点

      * @return 根节点信息

      */

     public static List<Menu> getChildrens(Menu root, List<Menu> all) {

         List<Menu> children = all.stream().filter(m -> {

             return Objects.equals(m.getParentId(), root.getId());

         }).map(

                 (m) -> {

                     m.setChildList(getChildrens(m, all));

                     return m;

                 }

         ).collect(Collectors.toList());

         return children;

     }

      * @param parentId 父节点id

      * @param menus 菜单集合

      * @return 返回id等于parentId的子孙节点树结构 （不包含id等于parentId的节点）

     public static List<Menu> getTree(Integer parentId, List<Menu> menus) {

         //获取父节点

         List<Menu> tree = menus.stream().filter(m -> Objects.equals(parentId,m.getParentId())).map(

                     m.setChildList(getChildrens(m, menus));

         return tree;

     public static void main(String... args) {

         //模拟从数据库查询出来

         List<Menu> menus = Arrays.asList(

                 new Menu( 1 , "0-1" , 0 ),

                 new Menu( 2 , "0-1-2" , 1 ),

                 new Menu( 3 , "0-1-2-3" , 2 ),

                 new Menu( 4 , "0-1-2-4" , 2 ),

                 new Menu( 5 , "0-1-2-5" , 2 ),

                 new Menu( 6 , "0-6" , 0 ),

                 new Menu( 7 , "0-6-7" , 6 ),

                 new Menu( 8 , "0-6-8" , 6 ),

                 new Menu( 9 , "0-6-7-9" , 7 ),

                 new Menu( 10 , "0-6-7-10" , 7 ),

                 new Menu( 11 , "0-11" , 0 ),

                 new Menu( 12 , "0-11-12" , 11 )

         );

         List<Menu> tree = getTree( 1 ,menus);

         System.out.println( "-------转json输出结果-------" );

         System.out.println(JSONUtil.parseArray(tree).toString());

}